This invention relates generally to a development apparatus that employs magnetic toner, and, more particularly, relates to development apparatus that develops an image by transporting single component magnetic toner utilizing a development member comprising a combination of an elastic or elastomeric layer and a magnetic field forming layer.
Development apparatus known in the art utilizes the single magnetic brush development method, and one such example is disclosed in U.S. Pat. No. 4,121,931. In this patent, the transport development roller member comprises a magnetic brush in the form of a magnetic roll formed on a nonmagnetic cylindrical sleeve, which is utilized to transport single component magnetic toner to perform image development on a image receptor member or latent image carrier. In another disclosure, Japanese patent 60-19506 discloses a development roller member comprising a nonmagnetic cylindrical center with an attached elastic conductive roller with an internal fixed or rotatable magnet for the transport of a single component magnetic toner wherein the development roller is placed in pressure contact with a latent image receptor or carrier.
Improvements over the years have been made on single component magnetic brush development systems and improved methods for development have been offered. One such improvement is disclosed in U.S. Pat. No. 4,564,285 wherein a transport development roller member comprises a nonmagnetic cylindrical sleeve with a magnetic roller formed internally of the sleeve, and a floating electrode is formed on its outer surface for the transport of single component magnetic toner resulting in enhanced picture quality of line images and solid images upon latent image development. Also, in Japanese laid open publication No. 59-119371, there is shown a development roller member comprising an insulating layer formed on a conductive base member with a plurality of dispersed minute electrodes formed on the surface of the insulating layer. Transport of single component magnetic toner by the development roller is accomplished with a magnetic field formed either in the insulating layer or in the dispersed electrodes and development of a latent image is accomplished by placing the development roller in engagement or contact with or in proximity to a latent image receptor or carrier. Further, U.S. Pat. No. 4,851,874 discloses a magnetic brush development roller for developing a latent image formed on an endless latent image receptor or carrier.
However, among these prior technologies employing magnetic toner development systems, albeit a single component magnetic brush development system or a conventional toner feed development system, the utilization of a development roller constructed of a cylindrical sleeve and an associated magnetic roller is complicated to fabricate, large in size and resulting in a costly component for use in image forming and reproducing apparatus. Further, because the threshold of miniaturization of the pole pitch is low, it is difficult with these development apparatus to form a thin and uniform toner layer on the surface of development roller. Since the leakage magnetic flux of the magnetic development roller cannot be sufficiently maintained on the development sleeve, a sufficiently high toner retention force cannot be maintained on the development sleeve causing toner scattering and image fogging in non-image portions. Also, there are many factors affecting picture quality deterioration, such as, nonuniform density of image toning and the formation of tails at the edges of the latent image caused from magnetic field variations in the magnetic development roller. Also, with respect to a development method that provides for the transport of toner in a thin layer on the surface of a magnetic development roller, deterioration in picture quality occurs in accordance with magnetic field variations over the magnetic roller. Also, the development apparatus of this type must be made larger in order to accommodate a latent image receptor or carrier of the endless belt type.
Also, the latter examples of prior technology relating to floating electrode structures have the problem in that it is difficult to form an insulation layer with minute magnets dispersed throughout its surface so that the cost of manufacturing are high. Also, since the magnetic force applied to the toner layer formed on the roller will be nonuniform, transported toner that is uncharged or having polarity different from normal polarity is developed, i.e., deposited also in the non-image portions of the latent image on the latent image carrier, which is known in the art as "fogging". While toner deposited in the non-image areas is not generally transferred to the recording medium, such as, in electrophotography, such deposited toner represents unnecessary waste, which is not only uneconomic, but also requires the use of a large waste toner container in the development apparatus increasing the overall size of the image forming apparatus. In addition, even when charged toner having normal polarity contacts the latent image carrier, toner whose amount of charge is relatively large compared to the unit bulk charge results in adherence to the non-image portions because of the mirror image force and becomes a principal cause of fogging that also remains on the recording medium.
In another aspect relative to the design of development apparatus of the prior art, there is known in Japanese laid open publication 64-65579 the use of a tubular membrane member rotatably supported on a drive roller wherein the membrane member has an ID larger than the OD of the drive roller so that the membrane member possesses surplus peripheral length relative to its drive roller. However, with this particular development apparatus design, there are difficulties in rendering the amount of transported toner uniform because the force that retains the toner on the development member depends on both the electrostatic image force and the adhesive force holding the transported toner. Also, when the toner is developed on a latent image carrier, such as, a light sensitive member or photoreceptor, uncharged toner and toner whose polarity is not normal or proper are deposited in the non-image portions, and, as a result, the only images that could be produced are those with highly conspicuous fogging, i.e., the state where toner adheres to the non-image portions, on the latent image carrier. Although images without fogging were obtained on the recording medium because only normal polarity toner was transferred to the recording medium, a substantial part of toner is not transferred to develop the latent image and, therefore, is unnecessarily wasted, which is not only uneconomical, but also requires sufficient amount of dedicated space in the waste toner receptacle resulting in larger overall size for the image forming apparatus.
Thus, it is an object of this present invention to provide development apparatus having a development member that provides for enhanced development of latent images on latent image carriers utilizing single component magnetic toner with little nonuniformity in variation in image density and without fogging effects by providing for stabilized transport of uniform amounts of toner by the toner development member.
Another object of this invention is the provision of a toner development apparatus having at least a combination elastic layer and magnetic field forming layer which are elastically displaceable and improve image quality and development properties.
A further object of this invention is the provision of a toner development apparatus that provides for enhanced picture quality having high resolution.
Another object of this invention is the provision of a toner development apparatus of simple construction, smaller size and reduced cost.